Variable sound level buzzer having resistance controlled winding



April 1, 1969 w u m 7, L 6 3 3 H. E. WEST VARIABLE SOUND LEVEL BUZZERHAVING RESISTANCE CONTROLLED WINDING Filed May 25, 1967 INVENTOR. HAROLDE. WEST 324 ATTORNEY United States Patent 3,436,759 VARIABLE SOUND LEVELBUZZER HAVING RESISTANCE CONTROLLED WINDING Harold E. West, Du Quoin,Ill., assignor to P. R. Mallory & Co., Inc., Indianapolis, Ind., acorporation of Delaware Filed May 23, 1967, Ser. No. 640,666 Int. Cl. Gk9/12 US. Cl. 340-388 8 Claims ABSTRACT OF THE DISCLOSURE A bifilarwinding is wound around a coil bobbin through which a pole piece isextended. A resistive element controls the voltage in one of the coilsof the :bifilar windings such that a magnetic flux is generated in thepole piece to attract an armature associated with the coil bobbin andpole piece. v

Variable sound level buzzers, prior to this invention, for the most partutilized a set screw in conjunction with a pole piece to vary the soundlevel. A hole was tapped through a pole piece and a threaded screw, withone end attached to an operating lever, was inserted into it. The otherend of the screw closed or widened the armature air gap through theengaged thread. Such closing and widening of the air gap controlled thebuzzer sound level. There were certain mechanical disadvantages in thisarrangement, among which were, variations in the torque, over life, etc.

The present invention is concerned with an entirely different approachto varying the sound level of buzzers and has as one of its objects theprovision of a variable sound level buzzer wherein the sound level iscontrolled by electromagnetic means.

Another object of the invention is the provision of a variable soundlevel buzzer wherein a bifilar wound coil and bobbin is used to controlthe sound level.

Another object of the invention is the provision of a variable soundlevel buzzer wherein a resistive element with a contact slider attachedto a control arm is used.

Still another object of the invention is the provision of a variablesound level buzzer wherein the resistive element is used to control themagnetic flux generated by the bifilar coils at a pole piece head toattract the armature.

Yet another object of the invention is the provision of a variable soundlevel buzzer wherein a time delayed signal is provided.

Still another object of the invention is the provision of a variablesound level buzzer having a thermistor connected across the bifilarwindings to achieve a time delayed signal.

With the above and other objects in view, which will appears as thedescription proceeds, this invention resides in a novel variable soundlevel buzzer substantially as described herein and more particularydefined by the appended claims, it being understood that such changes inthe precise embodiment of the invention here disclosed may be made ascome within the scope of the claims.

In the drawings:

FIGURE 1 is a perspective view of the novel buzzer showing the bifilarwinding;

FIGURE 2 is a schematic showing the wiring in relation to the resistancecontrol element in conjunction with the armature and the pole piece; and

FIGURE 3 is a schematic of another embodiment of the buzzer showing theuse of the thermistor for the time delayed signal.

Generally speaking, the objects of the invention are 3,436,759 PatentedApr. 1, 1969 accomplished by providing a variable sound level buzzerwherein the sound level is controlled by electromagnetic means. Aresistive element serves to control the magnetic flux that is generatedin the buzzer pole piece, so as to attract the armature through the polepiece. More particularly, a variable buzzer assembly having an armatureand a pole piece with a special wound coil and bobbin, and a resistanceelement with a contact slider attached to a control arm is provided.When the resistance element is open, the voltage across each section ofthe bifilar winding is equal, but of opposite phase, so that no magneticflux is gentrated at the pole piece head to attract the armature. As theresistance of one winding is decreased, the voltage of the windings nolonger oppose each other, magnetic flux is generated in the pole piece,the armature is attracted to the pole piece, and the sound level isincreased from zero to a maximum level.

In another embodiment, a thermal resistance element, such as athermistor, is connected across one of the windings for incorporating atime delayed signal in the buzzer.

Referring now to FIGURES 1 and 2, numeral 10 indicates the variablesound level buzzer of the present invention. A coil bobbin 11 isdisposed within a U-shaped armature 12 having sides 13' and 14 andbottom portion 15. A pole piece 16 extends through a bore 17 of thebobbin. Included as part of the pole piece is a head portion 18 throughwhich the side 14 of the armature is vibrated, side 14 thus serving asthe vibrating leaf of the armature. It is noted that there is an air gap19 between the head of the pole piece and side 14 of the armature.

The coil bobbin 11 contains a bifilar winding 20 disposed betweenretaining rims 21 and 22. The bifilar winding includes induction coils23 and 24 each having start and finishes 23 and 23", 24 and 2.4"respectively. As shown, variable resistance element 25 is connected inseries with the coils across the start 24 of coil 24 and the junction 26of the coils at their ifiniSh. As shown, a suitable voltage is appliedacross lines L and L The simplicity of operation of the buzzer lies inthe bifilar winding and the resistive control element 25. When theresistance element 25 is open, as shown in FIGURE 2, the current willflow through the coils, the voltage across each coil being equal but ofopposite phase. Thus, no magnetic flux will be generated at the head 18of the pole piece to attract the armature and cause it to vibrate. Asthe resistance is decreased through the manual setting of control arm27, current begins to flow through the resistance circuit 28 such thatthe opposing voltage in coil 24 is decreased. Thus, magnetic flux isgenerated in the pole piece from zero to a maximum level resulting in awhisper soft to a maximum loudness in the buzzer. Such maximum level isdetermined by customer demand.

Referring to FIGURE 3, there is shown another embodiment of theinvention wherein a time delayed signal is achieved. In householdappliance use, for example, a one-minute signal of the buzzer at thework end cycle is often objectionable, but is the minimum time the timerclock cam can provide. To overcome this objection, the present buzzerprovides a thermal sensitive resistance element, such as a thermistor29, connected in series across coil 24 in place of variable resistor 25.Preferably the thermistor is encapsulated within the bobbin by somesuitable means such as tape 30. The thermistor will have a certainresistance at room temperature, for example, 7000 ohms. The oppositephase voltage across it will heat the thermistor and lower itsresistance to 2000 ohms, for example, in a given time45 seconds, forexample. At this condition, the buzzer will then signal.

From the foregoing description it will be apparent to those skilled inthe art that this invention provides a J new and useful variable levelsound buzzer. Accordingly, it is contemplated that the scope of theinvention is to be determined from the claims appended hereto.

What is claimed is:

1. In a variable sound level buzzer having a coil bob bin disposedwithin an armature and having a pole piece for controlling the vibrationof said armature, a bifilar winding wound on said bobbin to form saidcoil, a source of voltage applied to each of the coils of said windingsuch that when current is passed through said coils the magnetic fluxinduced by said coils oppose each other, a variable resistance elementin series with said coil windings whereby the current in one of saidcoils can be 'varied from zero to a maximum such that the magnetic fluxgenerated by the other of said coils can be made to attract saidarmature through said pole piece.

2. A variable sound level buzzer according to claim 1, in which saidvariable resistance element is manually controlled.

3. A variable sound level buzzer according to claim 1, in which saidresistance element is thermally controlled.

4. A variable sound level buzzer according to claim 1, in which saidresistance element is a thermistor.

5. A variable sound level buzzer comprising a U- shaped armature, a coilbobbin disposed within said armature, a pole piece extending through abore of said bobbin, said pole piece being mounted onone side of saidU-shaped armature, there being an air gap betweenthe other end of saidpole piece and the other sideof said armature, a bifilar winding woundon said bobbin to form said coil, a source of voltage applied to each ofthe coils of said winding such that when current is passed through saidcoils the magnetic: flux induced by said coils oppose each other, avariable resistance element in series with said coil windings wherebythe current in one of said coils can be varied from zero to a 4 vmaximum such that the magnetic flux generated by the other of said coilscan be made to attract said armature through said pole piece.

6. A variable sound level buzzer according to claim 5, in which saidvariable resistance element is manually controlled. 1

7. A variable sound level buzzer according to claim 5, in which saidvariable resistance element is a thermistor.

8. A variable sound level buzzer comprising a U- shaped armature, "acoil vbobbin disposed within said bobbin, a pole piece extending througha bore of said bobbin, said pole piece being mounted at one side of saidU-shaped armature, there being an air gap between the other end of saidpole piece and the other side of said armature, a bifilar winding woundon said bobbin to form said coil, a source of voltage applied to each ofthe coils of said winding such that when current is passed through saidcoils the magnetic flux induced by said coils oppose each other, athermistor in series with said coil windings whereby the current in oneof said coils can be varied from zero to a maximum such that themagnetic flux generated by the other of said coils can be made toattract said armature through said. pole piece, said thermistor beingencapsulated within said JOHN W. CALDWELL, Primary Examiner.

HAROLD J. PITTS, Assistant Examiner.

. US. Cl. X.R. 340384

